It has been a common practice for readers of paper documents to mark up the documents with annotations. The annotations may be handwritten alphanumeric characters, punctuation marks, arbitrary symbols (e.g., smiley faces), underlining, enclosures (e.g., ovals), highlighting, and so on, which are generally referred to as “freeform ink.” Readers annotate documents for a variety of reasons such as to mark important points for rapid recall (e.g., a student preparing for a test), to show needed revisions to the document (e.g., a proofreader), and to add succinct summaries of paragraphs. Many readers consider the ability to annotate a document to be important to the effective reading and processing of the content of a document.
Because of this importance, electronic document systems, such as word processing systems, also allow users to annotate electronic documents. Initially, electronic document systems allowed users to select an annotation mode, select a location in a document for the annotation, and enter the text of the annotation (e.g., via a keyboard). The text of each annotation may be stored as part of the document, much like the text of footnotes. When the document is displayed, the text of the annotation might be displayed in a margin near the location for that annotation.
Although text-based annotations can be useful, they are not nearly as expressive as the freeform ink of paper documents. Several systems have been developed to support annotation of electronic documents using “freeform digital ink.” Some annotation systems have generated an electronic printout of a document, displayed that electronic printout, and allowed a user to annotate the pages of the documents using a digital pen. The user would use the digital pen to add the freeform digital ink near the associated text. Such annotation systems associated each annotation with a location on a page of the electronic printout where the freeform digital ink was drawn, rather than with the associated text. If the layout of the document changed (e.g., because of printing in landscape mode rather than portrait mode), the annotations associated with a location of the prior layout would not line up with the associated text in the new layout.
One annotation system overcame the problem of this changed layout by associating annotations with the associated text within the electronic document. This annotation system would open and display an electronic document. When a user annotated the displayed document with a digital pen, the annotation system captured the digital ink of the annotation and associated the annotation with the specific displayed text of the document. If the layout of the document changed, the annotation system could display the digital ink of the annotation with the associated text.